The present invention relates to a developer used for making lithographic printing plates by silver complex diffusion transfer process.
Printing plates where silver images obtained by silver complex diffusion transfer process (DTR process) which is one of photographic reproduction methods are used as offset printing original plates are disclosed in Japanese Patent publication (Kokoku) Nos. 46-43132 and 48-30562. Furthermore, positive type printing original plate is mentioned in Japanese Patent Publication (Kokai) No. 49-55402 and negative type printing original plate is mentioned in Japanese Patent Publication (Kokai) Nos. 52-106902 and 52-112402.
According to a typical silver complex diffusion transfer process suitable for making these lithographic printing plates, a light sensitive material which comprises a support and a subbing layer which serves also as an anti-halation layer, a silver halide emulsion layer and a physical development nuclei layer provided on said support is exposed imagewise and developed, whereby silver halide of latent image area becomes black silver in the emulsion layer and simultaneously silver halide of non-latent image area is dissolved by the action of a silver halide complexing agent contained in a processing solution and diffuse to the surface of the light sensitive material. Thus, dissolved and diffusing silver complex salt is precipitated as silver image on the physical development nuclei in the surface layer by reducing action of developing agent. Following the development, if necessary, the material is subjected to a sensitizing treatment to increase ink receptivity of the silver image. Then, thus obtained lithographic printing plate is mounted on an offset printing machine and printing is carried out by transferring the inked image to a substrate.
Various properties required for such lithographic printing plate depend greatly upon plate making step, especially, developing step as well as on printing materials. That is, state of silver image formed by transfer development is one of the significant factors of influence on printing characteristics and important causes for the state of silver image are conditions for formation of transferred silver grains, for example, diffusion speed, stability and reduction rate of silver complex salt.
U.S. Pat. Nos. 4,297,429, 4,297,403 and 4,355,090 disclose that kind of silver halide solvent has an important effect on conditions for formation of transfer silver grains.
However, only selection of silver halide solvent cannot result in transfer silver grains of sufficiently high printing endurance.